This invention relates to a magnetic disc cartridge in which an extremely thin disc-shaped magnetic recording sheet is rotatably supported, and more particularly to such a cartridge in which the part adapted to contact the end of the spindle of the sheet rotating means is improved.
To read or write magnetic data on such a disc sheet, a read/write head is radially moved across the sheet while it is being rotated. If the sheet is irregularly rotated, however, the signal inputting or outputting operations are adversely affected. More specifically, a 3.5" magnetic disc cartridge has a central core through which the cartridge is coupled to a sheet rotating means. If the protective case or envelope enclosing the sheet is deformed, the central core may scratch the inner wall of the case. As a result, the sheet may not be rotated smoothly, and data loss may occur.
To eliminate these difficulties, a conventional magnetic disc cartridge has incorporated an abutment plate at the center of the inner wall of the case, adapted to contact the end of the spindle of the sheet rotating means. When the case wall confronting the sheet is curved or distorted inwardly towards the sheet, the end of the spindle abuts against the plate to prevent the scratching of the case wall by the central core.
The abutment plate is made up of an outer surface layer, and an intermediate base layer through which the surface layer is bonded to the inner wall of the case. The surface layer is made of material such as macromolecular polyethylene so that it is sufficiently durable (wear resistant) when contacted by the rotating end of the spindle. It is difficult to machine this surface layer. The base layer is made of relatively soft unwoven cloth of rayon or the like into which adhesive is impregnated. With such a construction the abutment plate is gradually but significantly indented by the end of the spindle, however, and the service life of the cartridge is thus relatively short.